Rib strain relief hole Q

[fairchild]

Here is my first test of my nose rib cutting jig. Cutting the MDF was a pain but the 3/8 by 1.5 carbide bit cut the aluminum like it wasnt even there. Hardly any force back on the tooling.
I have not been able to find a 1/4 bearing piloted bit locally -- so the area around the strain holes is too big of a radius at the moment. Once I get the 1/4 bit I can cut the jig tighter
there. This was a test in some unknown scrap 025. But here is my question ------

After the flanges are bent---- and I am looking at the area around those holes--- should the edges of the holes be kind of "tangent" to the edge of the sheet----
OR--- should the edge of the hole (or circular notch-) be intruding inboard of where the edge of the sheet would otherwise be if you didnt do a strain relief hole.......
Im kind of asking where the hole should be relative to the bend line I guess......

I think I remember in the A&P books and 4313 they show a box or pan being made and they make the holes big enough that the outer edge of the holes are inboard
of the bend lines. (by quite a bit) Maybe if someone can post a close up of what that area look like on a "good" rib that might be helpful.
I can post another photo after I bend the flanges and yall can tell me ifs ya likes it.... (or if its messed up---)

Tim

[Chris In Milwaukee]

Take a look at these two threads of mine and see if we’re on the same page.

https://bearhawkforums.com/forum/bea...ng-a-rib-party

https://bearhawkforums.com/forum/bea...-fluting-party

it covers the entire process I used to cut and bend my ribs. Might offer some insight.

So far your ribs look good. If the holes are the diameter called for in the plans and along the chord line (marked on the Mylar), then you’re good to go. If the holes are a little undersized, no big deal. Just a little extra weight is all.

~Chris

[BTAZ]

I believe you are talking about where the bent flange will end at the front by the nose?

I drilled those relief holes after the rough blanks were in the router blocks but before routing as my router bit was too large to route them in.

Alternatively, use a small round file to put the correct shape in the router form and then file them in after the blank has been routed but before you remove it.

Tangent at a minimum so err on the inset side

[Chris In Milwaukee]

Ah, if you're talking about the corners by the flange as BTAZ describes, then I think as long as you have a smooth curve you'll be find. No stress point. I've left mine rounded from the router bit as you have.

Are you talking about something like this?

Fig2-2.png

If that's the case, I'd say it's more of an issue if you were hand-cutting the ribs with snips and would terminate the cut in a corner. Then you'd certainly need to drill a stress relief hole.

[fairchild]

Chris--- YES-- thats the thing Im asking--- in the right color picture-- you see the hole encompases the entire area between the two 90 degree bend tangents.
i just wanted to make sire my hole correctly interrupts the bend line like its supposed to . I suppose if you had the hole (in your picture) further outboard--- the area where the
hole is in the pic would have metal which was trying to do a compound corner bend with a whole bunch of stretching trying to happen and a whole bunch of stress going along
with it. So It looks like the hole just subtracts out that area that would have otherwise been a funkey-stretchy-compound area.

I was planning on drilling my hole in the blank using one of the steel bushings in the cutting jig---- but half of the hole is cut away for the router so there is no way to hold
a bushing. I DO have a roper whitney foot punch that i could punch the holes in the blank before I use the cutting jig. I guess it would be a matter if I could figure an accurate
and repeatable way to locate the hole when I punch it. have to think about that.....

When I get the bending/flangeing tool made (next) I want to bend the test piece and see if the bend line and hole play well together.

I will read the suggested threads too !
Tim
(another pic once I bend/flange)

[Bcone1381]

Hey Santa...I want a Roper Whitney foot punch too!

[BTAZ]

You don't really need a drill bushing in the corner if you use a bit of care. I filed the corner as pictured and then used it to guide about a 3/16" drill bit. Load the blanks into the routing jig and drill the relief hole prior to finish routing.

[Chris In Milwaukee]

It's my opinion that the wide-radius cut that the router left behind is appropriate for the strain relief at this intersection, and no other action is needed. Anyone else have a different view on these corners?

[BTAZ]

I think either is fine from a crack prevention point of view but the relief hole makes it a bit easier to get the flange formed in the corner with less fuss.

But since it doesn't sound like it was an issue for you then I think it is down to personal preference.

The example we are discussing here is not the same as the "box corner" described in your post. That relief is there not just for crack prevention but also to accommodate the setback/material thickness to allow the two 90 degree bends to even "work".

[Chris In Milwaukee]

I concur. Just happens to be the clearest picture I was able to Google on short notice

[fairchild]

Got my portfolio today for my plan sheets. Looks good.....
I will post another pic when I get the bends made and throw it out for critique ! :-)
Thank
Tim